fix: copy websocket.AcceptOptions to avoid CompressionMode leak

[715d]

In serveWS, when a Safari user-agent is detected, the code mutates e.acceptOptions.CompressionMode directly to disable compression. Since e.acceptOptions is shared across all requests, this mutation leaks to subsequent non-Safari connections (they also get compression disabled). There is also a data race: concurrent WebSocket upgrades read and write the same struct field without synchronization.

I replaced the shared mutation with a per-request local copy. Non-Safari requests pass e.acceptOptions as-is (read-only). Safari requests shallow-copy the struct into a local variable and set CompressionDisabled on the copy. The shared e.acceptOptions is never modified after initialization.